Field of the Invention
The present invention relates to an organic light emitting diode display (OLED) and a method of driving the same. In particular, the present invention relates to an OLED with improved image quality.
Discussion of the Related Art
Recently, flat display devices, such as a plasma display panel (PDP), a liquid crystal display (LCD), and an organic light emitting diode display (OLED), have been researched.
Among the flat display devices, the OLED is a self-luminescent device and can have a thin profile because the OLED does not need a backlight that is typically used for the LCD.
Further, compared with the LCD, the OLED has advantages of excellent viewing angle and contrast ratio, low power consumption, operation in low DC voltage, fast response speed, being resistant to an external impact because of its solid internal components, and wide operating temperature range.
Particularly, since the manufacturing process of the OLED is simple, the production costs of the OLED can be lower than that of the LCD.
FIG. 1 is a view illustrating organic light emitting diodes and driving circuits arranged in respective pixel regions of an OLED according to the related art, and FIG. 2 is a timing chart of gate pulses and data signals applied to the driving circuits of FIG. 1.
Referring to FIG. 1, the related art OLED includes first and second organic light emitting diodes D1 and D2 and first and second driving circuits 11 and 12 to operate the first and second organic light emitting diodes D1 and D2, respectively, in a display region 10.
In detail, the first driving circuit 11 is connected to a first gate line GL1 and each data line DL and operates the first organic light emitting diode D1, and the second driving circuit 12 is connected to a second gate line GL2 and each data line DL and operates the second organic light emitting diode D2.
For brevity, the first and second driving circuits 11 and 12 are shown in FIG. 1. However, a plurality of driving circuits may be arranged below the first and second driving circuits 11 and 12, and thus a plurality of gate lines may be arranged below the first and second gate lines GL1 and GL2 connected to the first and second driving circuits 11 and 12.
A method of driving the OLED is explained below.
The method of driving the OLED includes sequentially supplying first and second gate pulses g1 and g2 to the first and second gate lines GL1 and GL2, respectively, and sequentially supplying first and second data signals d1 and d2 to each data line DL.
Referring to FIG. 2, during a frame interval, the first gate pulse g1 is supplied to the first gate line GL1 and then the second gate pulse g2 is supplied to the second gate line GL2.
Further, the first and second data signals are sequentially supplied to the data lines DL per horizontal period H.
Further, the first data signal d1 is supplied to the first driving circuit 11 during an overlapping section between the first gate pulse g1 and the first data signal d1, and the second data signal d2 is supplied to the second driving circuit 12 during an overlapping section between the second gate pulse g2 and the second data signal d2.
Further, the first organic light emitting diode D1 emits light in a light-emission section from a falling point of the first gate pulse g1 during the present frame to a rising point of the first gate pulse g1 in the next frame, and the second organic light emitting diode D2 emits light in a light-emission section from a falling point of the second gate pulse g2 in the present frame to a rising point of the second gate pulse g2 during the next frame.
As shown in FIG. 1, the first driving circuit 11 is supplied with the first data signal d1 by the first gate pulse g1, and the second driving circuit 12 is supplied with the second data signal d2 by the second gate pulse g2.
In detail, the first driving circuit 11 is supplied with the first gate pulse g1 from the first gate line GL1 and the first data signal d1 from the data line DL to make the first organic light emitting diode D1 emit light.
Then, the second driving circuit 12 is supplied with the second gate pulse g2 from the second gate line GL2 and the second data signal d2 from the data line DL to make the second organic light emitting diode D2 emit light.
Unlike an LCD in which a thin film transistor is turned on only during a relatively short time in one frame interval, the OLED includes a driving thin film transistor in each of the first and second driving circuits 11 and 12 and maintains a turn-on state during a relatively long time in one frame interval. Accordingly, the driving thin film transistor of the OLED is prone to deterioration.
Accordingly, a threshold voltage (Vth) of the driving thin film transistor may vary, and this variation may negatively affect the display quality of the OLED.
In other words, because of the variation in threshold voltage (Vth), a gray level different from the target gray level of a data signal may be displayed, and thus the display quality of the OLED may deteriorate.
Further, when the organic light emitting diodes D1 and D2 emit light continuously during a certain time, the threshold voltages of the organic light emitting diodes D1 and D2 may also vary. Accordingly, the brightness of the organic light emitting diode may be different from the target brightness, and the lifetime of the organic light emitting diode may be reduced.